Mr Zapatero hopes his Socialist Party will win four more years in office, having been swept to power in 2004.

The debate was Spain's first of this kind for 15 years.

It did not disappoint.

For 90 minutes the two leaders exchanged verbal blows over a range of issues, with tempers frequently fraying.

Exploiting terror?

"You lied. You fooled all the Spanish people. You toyed with the law," alleged Mr Rajoy, the leader of Spain's more conservative Popular Party.

He was referring to the fact that Mr Zapatero's government continued secret dialogue with the Basque separatist group Eta, after the gunmen broke a ceasefire in December 2006.

At the time, Mr Zapatero had insisted dialogue was no longer possible.

In response, a furious Mr Zapatero called the opposition "immoral", saying they had exploited the issue of terror for party political gain.

"You were the ones who lied," he said, in reference to 2004 claims by the Popular Party, which was in power at the time, that Eta was behind terrorist attacks on Madrid trains, despite early evidence Islamic extremists were to blame.

Slowdown

The other pivotal issue in Monday's debate was the economy, with the two leaders trading statistics and even producing graphs and charts to illustrate their points.

Mr Zapatero said Spain's economy had performed magnificently during his term.

An estimated 12 million viewers tuned in to Monday's debate

He pointed to job creation and overall growth that has far outstripped that of France, Germany, Britain and the United States.

But Mr Rajoy emphasised that a slowdown that has coincided with the start of this campaign, pointing to rising unemployment and sharp rises in the cost of basic food.

The verbal sparring continued after debating time had officially run out.

Mr Zapatero, whose Socialists took power in the wake of the 2004 Madrid bombings, currently has a lead of around four percentage points in the opinion polls.

But both parties will be watching closely to see what effect, if any, this showdown has had.